The present invention relates to a method and apparatus for optically detecting a defect in a sample surface and, more particularly, to an optical inspection method and apparatus suitable for detecting a recess or a flaw in the surface of a conventional magnetic disk and foreign matters adhered to both faces of a magnetic disk.
For example, Japanese Patent Application Laid-Open Publication No. 2002-257742 (hereinbelow, referred to as patent document 1) and Japanese Patent Application Laid-Open Publication No. 2008-268189 (hereinbelow, referred to as patent document 2) describe an apparatus for detecting a defect in a surface of a magnetic disk as a conventional continuous recording magnetic medium. The patent document 1 discloses a configuration of obliquely irradiating a rotating magnetic disk with a laser beam, forming an image by regular-reflection light from the surface of the disk on a detector having plural light receiving elements, and processing a detection signal of the light to detect a defect.
The patent document 2 discloses an inspection apparatus which obliquely irradiates a rotating magnetic disk with a laser beam, detects regular-reflection light and scatting light from the surface of the disk, and processes detection signals of the regular-reflection light and scattering light to detect and classify a defect in the surface of the disk.
The patent document 2 also describes that a mask is provided so that regular-reflection light does not enter a lens provided on the side of regular reflection from a substrate (disk) to thereby interrupt regular-reflection light other than scatting light. It also describes that a half mirror is provided in place of a mask, and regular-reflection light is reflected by the half mirror and detected by a detector.
As the recording capacity of a magnetic disk increases, the recording density of the magnetic disk becomes higher, the size of a defect to be detected is decreasing, and the number of kinds of defects to be detected is increasing.
To address such demands, the patent document 1 describes that an image of regular-reflection light from the surface of the disk which is obliquely irradiated with a laser beam is detected by “n” pieces of light receiving elements arranged linearly, and the size of a recessed or projected defect in the surface of a substrate is detected with high precision on the basis of detection signal levels of the light receiving elements. However, it is not considered that a smaller defect in the surface of the substrate, for example, a shallow flaw defect (shallow defect) or a defect on the inside of the substrate is detected so as to be discriminated from the other defects.
The patent document 2 describes that a substrate is illuminated from multiple directions, regular-reflection light and scattering light from the substrate is detected, the state of a wave in the substrate itself or a local wave is determined from the waveform of the detection signals, and a defect is detected from the state. However, it is not described that a smaller defect in the surface of the substrate, for example, a shallow flaw defect (shallow defect) or a defect on the inside of the substrate is detected so as to be discriminated from the other defects.
The patent document 2 also describes that a mask is provided so that regular-reflection light does not enter a lens provided on the side of regular reflection from a substrate (disk) to thereby interrupt regular-reflection light other than scatting light, and that a half mirror is provided in place of a mask, and regular-reflection light is reflected by the half mirror and detected by a detector. However, it is not considered that a smaller defect in the surface of the substrate, for example, a shallow flaw defect (shallow defect) or a defect on the inside of the substrate is detected so as to be discriminated from the other defects by using detection signals of scattering light around the regular-reflection light excluding the regular-reflection light and a detection signal of the regular-reflection light.